Objective To evaluate the value of non-invasive coronary flow reserve ( CFR ) for investigating the relationship between myocardial ischemia and coronary stenosis ,and the result after percutaneous coronary intervention ( PCI) in patients with unstable angina pectoris . Methods The rest blood flow spectrum and the maximum coronary diastolic blood flow spectrum were obtained respectively for 131 coronary artery lesions including the left anterior descending coronary artery ,the left circumflex coronary artery and the right coronary artery in 86 patients from the coronary artery flow imaging of transthoracic Doppler echocardiography ,then CFR was calculated . All patients were performed by coronary angiography . Patients with the rate of coronary stenosis > 70％ and CFR ≤ 2 .0 were treated by PCI . CFR was measured again at different intervals after PCI . Results ① As the degree of stenosis increased ,CFR decreased gradually .The coronary stenosis was negatively correlated with CFR ( r = - 0 .803 , P < 0 .001) . The sensitivity of CFR ≤ 2 .0 predicting coronary stenosis rate of more than 70％ was 82 .7％ ,the specificity was 87 .7％ . ② CFR of post-PCI was higher than that of per-PCI . With a follow-up of half a year ,CFR of all coronary arteries was greater than 2 .0(44/44) ,but restenosis occurred at one year after PCI in two left anterior descending coronary arteries . Conclusions Non-invasive CFR can evaluate the relationship between myocardial ischemia and coronary stenosis ,select indications for PCI and evaluate postoperative outcome for patients with unstable angina pectoris .